phy: cadence-torrent: Add enum for supported input reference clock frequencies

Torrent PHY supports different input reference clock frequencies.
Register configurations will be different based on reference clock value.
Prepare driver to support such multiple reference clock frequencies.

Signed-off-by: Swapnil Jakhade <sjakhade@cadence.com>
Reviewed-by: Kishon Vijay Abraham I <kishon@ti.com>
Link: https://lore.kernel.org/r/20210728145454.15945-4-sjakhade@cadence.com


Signed-off-by: Vinod Koul <vkoul@kernel.org>